Cookie实现购物车功能

public class Book implements Serializable{
    
    //因为对象传输需要实现序列化接口
    //后面代码中id作为Map的键，而键只能为String
    String id;
    String name;
    double price;
    
    public Book(String id, String name, double price) {
        this.id = id;
        this.name = name;
        this.price = price;
    }

    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public double getPrice() {
        return price;
    }
    public void setPrice(double price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "Book [id=" + id + ", name=" + name + ", price=" + price + "]";
    }
}

public class CartItem implements Serializable{
    
    private Book book;
    private int quantity;
    private double price;
    
    public Book getBook() {
        return book;
    }
    public void setBook(Book book) {
        this.book = book;
    }
    public int getQuantity() {
        return quantity;
    }
    public void setQuantity(int quantity) {
        this.quantity = quantity;
    }
    public double getPrice() {
        return book.getPrice() * quantity;
    }
    public void setPrice(double price) {
        this.price = price;
    }
    
    @Override
    public String toString() {
        return "CartItem [book=" + book + ", quantity=" + quantity + ", price=" + price + "]";
    }
}

public class Cart<K, V> implements Serializable{

    //键为书名id，储存实物
    private double totalPrice;
    private HashMap<String,CartItem> bookMap = new HashMap<String, CartItem>();
    
    public void addBook(Book book){
        //从购物车找对应书籍的购物项
        CartItem cartItem = bookMap.get(book.getId());
        //若没有该书的购物项，新建一个
        if(cartItem == null){
            cartItem = new CartItem();
            cartItem.setBook(book);
            cartItem.setQuantity(1);
            bookMap.put(book.getId(), cartItem);
        }else{
            cartItem.setQuantity(cartItem.getQuantity() + 1);
        }
    }
    public void deleteBook(Book book){
        CartItem cartItem = bookMap.get(book.getId());
        if(cartItem == null){
            //do nothing
        }else if(cartItem.getQuantity() == 1){
            bookMap.remove(book.getId());
        }else{
            cartItem.setQuantity(cartItem.getQuantity() - 1);
        }
    }
    public double getPrice(){
        //遍历购物车里的购物项
        for(Map.Entry set : bookMap.entrySet()){
            //String bookId = (String) set.getKey();
            CartItem cartItem = (CartItem) set.getValue();
            totalPrice += cartItem.getPrice();
        }
        return totalPrice;
    }

    public HashMap<String, CartItem> getBookMap() {
        return bookMap;
    }
    public void setBookMap(HashMap<String, CartItem> bookMap) {
        this.bookMap = bookMap;
    }
    public double getTotalPrice() {
        return totalPrice;
    }
    public void setTotalPrice(double totalPrice) {
        this.totalPrice = totalPrice;
    }
}

//往购物车添加书本
Cart cart = new Cart();
cart.addBook(new Book("1","且听风吟",10.5f));
cart.addBook(new Book("1","且听风吟",10.5f));
cart.addBook(new Book("1","且听风吟",10.5f));
cart.addBook(new Book("2","我们仨",5.5f));
cart.deleteBook(new Book("1","且听风吟",10.5f));
cart.deleteBook(new Book("2","我们仨",5.5f));
cart.deleteBook(new Book("3","解忧杂货店",20.5f));

//  -----------------------------购物车对象序列化------------------------[开始]
ByteArrayOutputStream bos= new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(bos);
oos.writeObject(cart);
String objectString = URLEncoder.encode(bos.toString("ISO-8859-1"),"UTF-8");
//  -----------------------------购物车对象序列化------------------------[完]    

//  -----------------------------给客户端添加cookie------------------------[开始]
response.setContentType("text/html;charset=UTF-8");
Cookie cookie = new Cookie("name", objectString);
cookie.setMaxAge(1000);
response.addCookie(cookie);
//  -----------------------------给客户端添加cookie------------------------[完]

Cookie[] cookies = request.getCookies();
if(cookies != null){
    for(Cookie cookieLoop : cookies){
        String name = cookieLoop.getName();
        String value = URLDecoder.decode(cookieLoop.getValue(), "UTF-8");
        if(name == "Cart"){
            ByteArrayInputStream bis = new ByteArrayInputStream(value.getBytes("ISO-8859-1"));
            ObjectInputStream ois = new ObjectInputStream(bis);
            try {
                Cart cart1 = (Cart) ois.readObject();
                HashMap cartMap = cart1.getBookMap();
                for(Object cartItem : cartMap.values()){
                    //遍历购物项并打印
                    System.out.println(cartItem.toString());
                }
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            }
        }
    }
}

CartItem [book=Book [id=1, name=且听风吟, price=10.5], quantity=2, price=0.0]
<!-- 剩下且听风吟 * 2 -->